Molecular sieve confinement metal propane dehydrogenation catalyst and preparation method and application thereof

Abstract

The invention discloses a molecular sieve confinement metal propane dehydrogenation catalyst as well as a preparation method and application thereof. The catalyst comprises a molecular sieve nanosheet carrier and a metal active component, the metal active component comprises a first metal and a second metal, the first metal exists in a molecular sieve pore channel in a confinement manner in a monatomic form, and the second metal is formed around the first metal and at least partially replaces a molecular sieve skeleton structure. According to the method, fluorine ions are used as a mineralizing agent and an auxiliary structure-directing agent, and rapid crystallization and morphology regulation and control of the molecular sieve are realized through a one-step hydrothermal method. The process is simple, convenient and green, the traditional complicated post-loading or complexing agent assistance route is abandoned, and the problems that the active center is easy to agglomerate and the synthesis pollution is serious are effectively solved. The obtained catalyst has the ultrathin diffusion advantage of nanosheets and the chemical anchoring stability of heteroatoms, and shows excellent activity, high propylene selectivity and long-period stability in a propane dehydrogenation reaction.

Description

Technical Field

[0001] This invention belongs to the field of catalytic conversion of alkane. Specifically, it relates to a molecular sieve-confined metal propane dehydrogenation catalyst, more specifically to a framework heteroatom anchored and stabilized highly dispersed platinum single-atom catalyst with molecular sieve confinement characteristics. It also relates to a method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization, as well as the catalyst for propane dehydrogenation to propylene prepared by this method and its application. Background Technology

[0002] Propylene is a high-value-added energy chemical product, considered a crucial raw material for extending China's chemical industry chain. Its downstream products are widely used in industry, agriculture, daily chemicals, medical devices, and scientific research, holding a key position in the national economy. For a long time, market expansion of polypropylene and other propylene derivatives has driven the growth in propylene demand, maintaining a rapid expansion trend in China's propylene industry.

[0003] Propylene production encompasses mainstream traditional processes and emerging targeted production technologies. Traditional processes include naphtha steam cracking, refinery catalytic cracking (FCC) separation, and heavy oil catalytic cracking (DCC). Emerging targeted production technologies include olefin disproportionation, methanol-to-olefins (MTP, MTO), and propane dehydrogenation (PDH). In recent years, coal chemical industry has been constrained by its inherent high energy consumption, high pollution, and high emissions; oil-based production has slowed due to refining scale reaching its limits. In contrast, direct propane dehydrogenation to propylene technology features a single feedstock, a single product, a single process, targeted synthesis, and easy reverse integration. It boasts high propylene yield, low investment intensity, high return on investment, and significant environmental and cost advantages, aligning better with the national clean energy development path and goals. Under the policy background of energy structure optimization and upgrading and diversified energy supply, it has a greater competitive advantage. Therefore, direct propane dehydrogenation to propylene is the optimal targeted propylene production process and the main direction for future propylene capacity expansion, representing a key technology for achieving efficient utilization of carbon-based energy.

[0004] Propane dehydrogenation is a strongly endothermic reaction that increases the number of molecules; both increasing temperature and decreasing pressure favor the forward direction of the dehydrogenation reaction. The CH bond energy of the propane molecule is high, resulting in low reactivity and requiring high energy for activation. The resulting olefins are more reactive than alkanes, readily undergoing further dehydrogenation to form coking species. This makes it difficult to coordinate improvements in conversion and selectivity, and the relatively low olefin yield drives the optimization of catalyst design.

[0005] Currently, industrially available propane dehydrogenation catalysts are mainly based on platinum (Pt) or chromium (Cr)-based materials, represented by UOP's Oleflex process and ABB Lummus's Catofin process, respectively. The application of chromium-based catalysts is limited due to environmental toxicity concerns; while platinum-based catalysts, although exhibiting high activity, are expensive and prone to side reactions such as hydrogenolysis during the reaction, leading to the formation of carbon deposits (coke) on the catalyst surface, which covers active sites and reduces activity. Therefore, frequent regeneration via chlorination combustion is necessary. Furthermore, under high-temperature reaction conditions, platinum species are prone to agglomeration and sintering, further resulting in catalytic activity loss and low production efficiency.

[0006] In propane dehydrogenation, platinum-based catalyst promoters commonly used in the process are concentrated in transition metals and rare earth metals. The second metal can form alloys or metal oxides with the host metal, preventing the aggregation of active metal atoms and thus improving dispersion; it can also increase the electron density of the active metal, thereby weakening its interaction with olefins, increasing the desorption rate of propylene, and inhibiting deep dehydrogenation and carbon deposition of propylene. Although bimetallic catalysts have shown potential to surpass monometallic catalysts, the introduction of a second metal and the complex synthesis process (such as the use of expensive organic templates and multi-step synthesis) further increase the production cost of the catalyst.

[0007] Molecular sieve materials, with their sub-nanometer ordered pore structure, excellent shape selectivity, and outstanding hydrothermal stability, have become indispensable catalytic materials in the petrochemical and fine chemical industries. In recent years, to further enhance the catalytic performance of reactions such as propane dehydrogenation, researchers have extensively focused on encapsulating metal active centers (such as platinum and palladium) within the pores or framework of molecular sieves to construct "metal@molecular sieve" confined catalytic systems. This strategy utilizes the spatial confinement effect of the molecular sieve framework, theoretically effectively inhibiting the migration, sintering, and aggregation of metal species under high-temperature reaction conditions, thereby significantly improving the thermal stability and lifetime of the catalyst. However, despite its promising prospects, existing metal@molecular sieve in-situ encapsulation strategies are still constrained by several key bottlenecks in their progress towards practical industrial applications.

[0008] Traditional in-situ encapsulation methods typically lack precise control over the microenvironment of metal species. Most methods rely solely on physical space to confine metal particles, lacking strong chemical bonds between the metal and the framework. In harsh high-temperature dehydrogenation reactions, metal atoms readily escape the pores and undergo secondary aggregation on the outer surface, leading to rapid catalyst deactivation. Furthermore, traditional single-atom synthesis often requires expensive organic ligands or complexing agents to stabilize the metal, which then need to be removed by high-temperature calcination, easily causing environmental pollution and framework collapse. To achieve high metal dispersion, existing technologies often require the introduction of expensive and complex organic ligands or complexing agents (such as ethylenediamine, thiols, etc.) to protect the metal precursor. This increases raw material costs, and these organic compounds are difficult to completely remove in subsequent processing; residual carbon species may cover active sites or even poison the catalyst.

[0009] Furthermore, the synthesis process of molecular sieve materials suffers from high energy consumption and is not environmentally friendly. Existing synthesis routes are generally characterized by cumbersome steps, long cycles, and heavy pollution. Traditional hydrothermal synthesis of pure silicon or high-silicon molecular sieves typically requires several days or even weeks of crystallization time, resulting in extremely low production efficiency and enormous energy consumption. The synthesis process often uses large amounts of organic template agents, which must be removed by subsequent high-temperature, long-term calcination. This process not only generates large amounts of greenhouse gases and harmful waste gases but also results in the discharge of large quantities of high chemical oxygen demand (COD) waste liquid.

[0010] Microporous structures suffer from severe diffusion limitations. Conventional microporous molecular sieves, due to their narrow pore size and long diffusion paths, experience significant mass transfer resistance to large molecular reactants or products within the pores. This results in the inability to fully utilize internal active sites, and products are prone to lingering within the pores, leading to side reactions and further shortening catalyst lifetime. Although research has been conducted on nanosheet or hierarchical porous molecular sieves, existing preparation methods often struggle to simultaneously achieve high crystallinity, ultrathin morphology, and high dispersion of single metal atoms in a single step. Multiple post-processing steps (such as acid-base etching) are typically required, which can easily damage the integrity of the molecular sieve framework.

[0011] In recent years, the inventors have conducted a series of studies on the preparation methods of molecular sieve confined catalysts for the direct dehydrogenation of propane to propylene. Through post-synthesis and ligand-protected in-situ synthesis, they have prepared confined CoOx / BEA (Chemical Engineering Journal, 2025, Vol. 519, 165035 pages) and metal-encapsulated PtZn@BEA (Journal of Energy Chemistry, 2021, Vol. 57, 92-98 pages) and Zn@MFI (Journal of Energy Chemistry, 2021, Vol. 63, 262-269 pages), respectively, achieving certain propane conversion and propylene selectivity. However, the production efficiency and reaction stability of these methods are still far from industrial scale-up.

[0012] Therefore, it is crucial to develop a simple and controllable preparation method that selectively modifies molecular sieves and introduces bimetallic active components to optimize the catalyst preparation process and enhance the reactivity of noble metal catalysts. Summary of the Invention

[0013] To address the aforementioned technical challenges, this invention proposes a novel strategy for fluoride ion-assisted rapid crystallization, providing a propane direct dehydrogenation molecular sieve-confined metal catalyst that balances propane conversion, propylene selectivity, and reaction stability, along with its preparation method and applications. This method eliminates complex organic complexing agents, utilizing the dual effects of fluoride ion mineralization and structure orientation to achieve the following breakthroughs in a one-step hydrothermal process: ① Atomic-level precise anchoring: Using framework heteroatoms as anchoring points, active metal (such as platinum) single atoms are firmly locked through chemical bonds, achieving absolute controllability and high stability of active sites; ② One-step morphology engineering: Directly growing ultrathin nanosheet structures, breaking diffusion limitations; ③ Green and minimalist process: Extremely fast crystallization speed significantly reduces energy consumption and waste emissions, providing a truly simple, controllable, and green new industrial preparation path.

[0014] This invention provides a molecular sieve-confined metal propane dehydrogenation catalyst, the catalyst comprising a molecular sieve nanosheet support and a metal active component, the metal active component comprising a first metal and a second metal, the first metal being confined in the molecular sieve channels in the form of single atoms, the second metal being formed around the first metal and at least partially replacing the molecular sieve framework structure; specifically, the second metal replaces silicon in the molecular sieve framework to obtain a framework-grafted metal hydroxyl species.

[0015] The first metal is selected from at least one of Pt, Pd, Ir, Rh and Ru, and the second metal is selected from at least one of Fe, Co, Zn, Cu, Mn, In and Ga.

[0016] According to the present invention, the loading of bimetals in the catalyst can be varied within a certain range. Based on the weight of the catalyst, the content of the first metal can be 0.01 wt% to 1 wt%, specifically including any one of 0.01 wt%, 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%, or a value within the range of any two of the above values, preferably 0.05 wt% to 0.5 wt%, more preferably 0.1 wt% to 0.4 wt%. The content of the second metal can be 0.1 wt% to 20 wt%, specifically including 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%. The values ​​are any one of the following: 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, or any combination of the above values, preferably 0.2 wt% to 10 wt%, more preferably 0.3 wt% to 6 wt%, with the remainder being a carrier (molecular sieve).

[0017] According to the present invention, the silica-to-alumina ratio (SAR) of the molecular sieve nanosheet support can be changed within a certain range, for example, greater than or equal to 50. The preferred molecular sieve is a high-silica molecular sieve (SAR = 50 ~ 1000+), and the most preferred catalyst is a pure silica molecular sieve (Si / Al = infinite).

[0018] A second aspect of the present invention provides a method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization, comprising the following steps: Step 1: Mix and stir the organic structural template agent, silicon source, and water; Step 2: Mix the aqueous solution of the fluoride ion mineralizing agent with the solution obtained in Step 1, and perform the first stirring and aging to obtain the synthetic sol; Step 3: Mix the aqueous solution containing the first metal precursor and the second metal precursor with the synthetic sol, and perform a second stirring and aging process to obtain a metal-containing synthetic sol; the first metal in the first metal precursor is selected from at least one of Pt, Pd, Ir, Rh and Ru; the second metal in the second metal precursor is selected from at least one of Fe, Co, Zn, Cu, Mn, In and Ga; Step 4: Perform hydrothermal crystallization on the metal-containing synthetic sol, then perform solid-liquid separation on the mixture obtained by hydrothermal crystallization, and then dry and optionally calcine the separated solid product to obtain a molecular sieve confined metal propane dehydrogenation catalyst.

[0019] According to a preferred embodiment of the present invention, the organic structural template agent is at least one selected from ethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

[0020] According to a preferred embodiment of the present invention, the silicon source is at least one selected from silica sol, tetraethyl orthosilicate, amorphous silica, fumed silica, and silicates.

[0021] According to a preferred embodiment of the present invention, the fluoride-containing mineralizing agent is at least one selected from ammonium fluoride, sodium fluoride, potassium fluoride, and calcium fluoride.

[0022] According to a preferred embodiment of the present invention, the molar ratio of the organic structural template agent (in molecules) to the silicon source (in SiO2) in the synthesis mother liquor, T / SiO2, is 0.05 to 0.4:1. This can be exemplified by any one of the following values, or a range consisting of any two of the above values: 0.05:1, 0.08:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, and 0.4:1. Preferably, T / SiO2 is 0.05 to 0.2:1.

[0023] According to a preferred embodiment of the present invention, the molar ratio of water to the silicon source (calculated as SiO2) in the synthesis mother liquor, H2O / SiO2, is 5 to 100:1. Examples include any one of the following values, or a range of any two of the above values: 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1, and 100:1. Preferably, H2O / SiO2 is 15 to 50:1.

[0024] According to a preferred embodiment of the present invention, the molar ratio of the ammonium fluoride (in molecules) to the silicon source (in SiO2) in the synthesis mother liquor, NH4F / SiO2, is 0.01 to 1:1. This can be exemplified by any one of the following values, or a range consisting of any two of the above values: 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, and 1:1. Preferably, the ratio of NH4F / SiO2 is 0.05 to 1:1.

[0025] According to the present invention, the mixing and stirring time in step 1 can be 1 to 12 hours, until the mixture is uniform.

[0026] According to the method of the present invention, the aging is carried out by dynamic stirring in an oil bath. Specifically, the conditions for the first stirring aging in step 2 include: a temperature of 25~100 ℃, preferably 80~90 ℃, and a time of 1~24 hours, preferably 8~16 hours; the conditions for the second stirring aging in step 3 include: a temperature of 25~100 ℃, and a time of 1~24 hours, preferably 8~16 hours.

[0027] According to the present invention, the metal precursor can be an organic or inorganic precursor of a metal. Specifically, the first metal precursor is at least one of an inorganic acid, inorganic salt, inorganic acid salt, inorganic complex, organic acid, organic acid salt, organic complex, oxide, and hydroxide of a first metal; the second metal precursor is at least one of an inorganic acid salt, organic acid salt, oxide, and hydroxide of a second metal; wherein the inorganic acid salt is preferably a nitrate, hydrochloride, or sulfate, and the organic acid salt is preferably at least one of acetate and gluconate.

[0028] More specifically, for the first metal, the precursor of platinum can be selected from chloroplatinic acid, platinum nitrate, platinum chloride, dichlorotetraammineplatinum, and platinum acetylacetonate; the precursor of palladium can be selected from chloropalladium acid, palladium nitrate, palladium acetate, tetraamminepalladium nitrate, potassium tetrachloropalladate, and palladium acetylacetonate; the precursor of ruthenium can be selected from ruthenium trichloride and ruthenium acetylacetonate; the precursor of rhodium can be selected from rhodium trichloride and rhodium acetylacetonate; and the precursor of iridium can be selected from chloroiridic acid and potassium hexachloroiridate.

[0029] For the second metal, the precursor of iron is preferably an inorganic acid salt of iron, specifically ferric nitrate, ferric sulfate, ferrous sulfate, ferrous nitrate, ferric chloride, or ferrous chloride, with hydrated ferric nitrate being the most preferred; the precursor of cobalt is preferably an inorganic acid salt of cobalt, specifically cobalt sulfate, cobalt nitrate, or cobalt chloride; the precursor of zinc is preferably an inorganic acid salt of zinc, specifically zinc nitrate, zinc sulfate, or zinc chloride, with hydrated zinc nitrate being the most preferred; the precursor of manganese is specifically manganese gluconate, manganese sulfate, manganese nitrate, or manganese chloride, preferably an organic acid salt of manganese, with manganese gluconate being the most preferred; the precursor of indium is preferably an inorganic acid salt of indium, specifically indium nitrate or indium chloride, with hydrated indium nitrate being the most preferred; the precursor of gallium is preferably an inorganic acid salt of gallium, specifically gallium nitrate or gallium chloride.

[0030] According to the present invention, each step in step 4 can be performed using relatively conventional methods. Specifically, the conditions for hydrothermal crystallization include: a temperature of 90~200 ℃, preferably 160~180 ℃, and a time of 1~7 days, preferably 2~4 days, and most preferably 3 days.

[0031] The drying temperature can be 60~120 ℃, and the time can be 6~12 hours, specifically 80 ℃ for 12 hours.

[0032] The roasting temperature can be 500~700 ℃, and the time can be 2~10 hours. Specifically, it can be heated from room temperature to 550 ℃ at a rate of 2 ℃ / min and held for 6 hours, with the roasting atmosphere being air.

[0033] A third aspect of the present invention provides a molecular sieve-confined metal propane dehydrogenation catalyst prepared by the above method.

[0034] The preparation method of this invention uses fluoride ions as both a mineralizer and an auxiliary structure-directing agent, achieving rapid crystallization and morphology control of molecular sieves through a one-step hydrothermal method. Its core lies in eliminating the need for organic complexing agents, utilizing the isomorphic substitution sites of framework heteroatoms to in-situ anchor highly dispersed platinum single atoms, and simultaneously inducing the growth of the molecular sieve into an ultrathin nanosheet structure. This process is simple and environmentally friendly, abandoning the traditional cumbersome "post-loading" or "complexing agent-assisted" routes, and effectively solving the problems of easy aggregation of active centers and high synthesis pollution. The resulting catalyst combines the diffusion advantages of ultrathin nanosheets with the stability of heteroatom chemical anchoring: the extremely short mass transfer path significantly reduces diffusion resistance, while the strong heteroatom-framework oxygen-platinum chemical bonds achieve atomic-level high dispersion and anti-sintering properties of platinum species. This catalyst exhibits excellent activity, high propylene selectivity, and long-term stability in propane dehydrogenation reactions.

[0035] A fourth aspect of the present invention provides the application of the above-described molecular sieve-confined metal propane dehydrogenation catalyst in the oxygen-free dehydrogenation of propane to propylene.

[0036] A fifth aspect of the present invention provides a method for the oxygen-free dehydrogenation of propane to propylene, the method being carried out in a fixed-bed reactor, wherein the catalyst bed of the fixed-bed reactor is packed with the aforementioned molecular sieve-confined metal propane dehydrogenation catalyst, the method comprising the following steps: Before the reaction, the catalyst is pretreated with a reducing gas or an inert gas, and then the raw material gas is introduced to carry out the propane dehydrogenation reaction.

[0037] The reaction process for producing propylene from propane through oxygen-free dehydrogenation provided by this invention is as follows (including side reactions):

[0038] According to a preferred embodiment of the present invention, the reducing gas is selected from at least one of diluted hydrogen and diluted carbon monoxide, and the inert gas is selected from at least one of nitrogen, argon and helium.

[0039] According to a preferred embodiment of the present invention, the pretreatment temperature is 300~600 °C and the time is 0.5~4 hours.

[0040] According to a preferred embodiment of the present invention, the feed gas consists of propane and a balance gas, wherein the balance gas is preferably at least one of nitrogen, argon, and helium, and the concentration of propane in the feed gas can be 10-100 wt%. In order to further improve the conversion rate, selectivity, space-time yield, and catalyst lifespan and reduce the amount of catalyst used, the preferred volume concentration of propane is 50-100 wt%, more preferably 100%.

[0041] According to the present invention, the temperature of the propane dehydrogenation reaction can be 300~650 °C, and the pressure can be 0~0.2 MPa. In order to further improve the conversion rate, selectivity, space-time yield, and catalyst lifespan and reduce catalyst dosage, the preferred reaction temperature is 500~600 °C, more preferably 550~600 °C, for example, 500 °C, 520 °C, 550 °C, 570 °C, 575 °C, 580 °C, and 600 °C.

[0042] According to the present invention, the propane mass hourly space velocity (HHSV) for the direct dehydrogenation of propane can be 1 to 100 h⁻¹. -1 To further improve the conversion rate, selectivity, space-time yield, and catalyst lifetime while reducing catalyst dosage, the preferred propane mass hourly space velocity is 4-60 h⁻¹. -1 For example, it could be 4 h -1 8 h -1 12 h -1 16 h -1 20 h-1 24 h -1 28h -1 32 h -1 40 h -1 50 h -1 60 h -1 .

[0043] The amount of catalyst can be varied within a wide range. For example, the amount of catalyst is 0.05~0.4 g, preferably 0.1~0.3 g, and more preferably 0.1~0.15 g.

[0044] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: According to the method of the present invention, an active component is introduced in situ during the synthesis of nanosheet molecular sieves to prepare a molecular sieve-confined metal propane dehydrogenation catalyst. The preparation process is simple and the process flow is easy. There is no need to perform post-processing operations on the molecular sieve support, avoiding the use of strong acid reagents, avoiding equipment corrosion, and reducing environmental pollution. There is no need to use additional loaded organic ligands to complex metal ions, reducing the synthesis cost, and high-content metal components can be introduced.

[0045] This invention employs a specific catalyst preparation method, introducing inexpensive and readily available heteroatoms (i.e., a second metal) to replace silicon atoms in the molecular sieve framework. Due to the difference in electronegativity and atomic radius between the heteroatoms and silicon, local electronic defect sites or strongly polar sites are formed within the framework. The catalytically active metal center (such as platinum atoms) is firmly anchored by chemical bonds through these heteroatom sites. This chemical binding energy is significantly higher than the physical adsorption energy of simple silicon-oxygen bonds, firmly locking the active metal (such as platinum) single atoms within confined channels. This fundamentally overcomes the common problem of single-atom catalysts easily migrating and agglomerating into nanoparticles at high temperatures or during reactions, significantly improving the catalyst's thermal stability and long-term stability. Even in high-temperature dehydrogenation environments above 550°C or even 600°C, the active metal (such as platinum) atoms remain in situ, effectively solving the common "high-temperature sintering" problem of traditional catalysts. This framework heteroatom anchoring strategy achieves ultra-high atomic utilization of active metal (such as platinum) species, ensuring that each active metal (such as platinum) atom is in an active state, avoiding the waste of "dead volume" or inactive metals in traditional impregnation methods.

[0046] This invention introduces metal precursors directly during the gelation stage with the assistance of fluoride ions, eliminating reliance on expensive complexing agents. This not only reduces raw material costs but also avoids batch-to-batch quality variations caused by slight differences in complexing agent ratios, significantly improving the stability of industrial mass production. It abandons the traditional two-step method of "synthesizing the carrier first, then loading the metal," utilizing the mineralization-inducing effect of fluoride ions on silicon species to simultaneously assemble the framework of heteroatoms and active metal (such as platinum) atoms in situ while forming the unique morphology of nanosheets. This "one-pot method" greatly shortens the preparation cycle and improves production efficiency. As a highly efficient mineralizing agent, fluoride ions significantly lower the nucleation barrier, accelerating the condensation and rearrangement of silicon species, resulting in a substantial reduction in crystallization time and rapid crystallization. This not only saves energy but also helps control crystal growth kinetics and prevents excessive crystal growth. The structure-directing effect of fluoride ions restricts the growth of molecular sieves along specific axes, forming ultrathin nanosheet structures. This structure greatly shortens the diffusion path of reactant and product molecules within the microporous channels, significantly reducing mass transfer resistance. It is particularly suitable for macromolecular catalytic reactions and can effectively solve the bottleneck of "diffusion limitation" in traditional microporous molecular sieves.

[0047] This invention successfully optimized and prepared a bimetallic propane dehydrogenation catalyst with a molecular sieve confinement possessing high framework heteroatom content, low noble metal loading, and a suitable bimetallic ratio. The propane dehydrogenation reaction sites provided by this invention differ from other platinum-based zeolite molecular sieves; their catalytic activity is driven by ultra-small structural units of highly dispersed and stable framework heteroatoms-oxygen-highly dispersed platinum single atoms, rather than a single noble metal component. Framework heteroatoms not only act as anchoring sites but also play a regulatory role electronically. Through the electronic feedback of heteroatoms, the outer electron cloud density of the platinum active center can be fine-tuned, optimizing its desorption capacity for hydrogen atoms and its selectivity for propylene. This fundamentally suppresses deep cracking side reactions in the dehydrogenation reaction, achieving a dual enhancement of activity and selectivity. Simultaneously, framework heteroatoms assist in the desorption and catalytic cycle closure by promoting the spillover and recombination of adsorbed hydrogen species, making it more favorable for the target dehydrogenation reaction and less favorable for side reactions.

[0048] In summary, the catalyst of this invention constructs a novel single-atom active structure through a unique framework heteroatom anchoring mechanism, effectively breaking the "seesaw" effect between conversion and selectivity in the propane dehydrogenation reaction. Experiments show that this catalyst can simultaneously achieve a propane conversion of >50% and a propylene selectivity of >95%, significantly outperforming traditional industrial catalysts and exhibiting excellent single-pass yield. This is due to the strong chemical bond anchoring effect, which makes it extremely difficult for platinum single atoms to migrate and aggregate at high temperatures; combined with the unique nanosheet structure of the molecular sieve, the product diffusion path is significantly shortened, effectively inhibiting the carbon deposition caused by deep dehydrogenation, allowing the catalyst to maintain reaction stability and high activity during long-term operation. The preparation method is simple, reproducible, and eliminates expensive organic complexing agents; using low-cost pure silica zeolite molecular sieves as a carrier, combined with fluorine-assisted rapid crystallization technology, significantly reduces raw material costs and energy consumption, and the reaction conditions are mild and controllable, possessing extremely high value for large-scale industrial application.

[0049] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0050] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0051] Figure 1 The image shows the XRD pattern of the catalyst sample from Example 1.

[0052] Figure 2 This is a SEM image of the catalyst sample from Example 1.

[0053] Figure 3 This is a TEM image of the catalyst sample from Example 1.

[0054] Figure 4 The images show the CO adsorption infrared spectra of the catalyst samples from Example 1 and Comparative Example 1.

[0055] Figure 5 This is a single-pass stability evaluation diagram of the direct propane dehydrogenation reaction of the catalyst sample in Example 1.

[0056] Figure 6 This is a graph showing the cyclic stability evaluation of the direct propane dehydrogenation reaction of the catalyst sample in Example 1. Detailed Implementation

[0057] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0058] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0059] Example 1

[0060] A platinum-iron bimetallic catalyst confined within pure silicon nanosheet molecular sieves was synthesized using ammonium fluoride as a mineralizing agent and hydrated ferric nitrate and chloroplatinic acid as inorganic iron and platinum sources, respectively. This catalyst was named catalyst Pt. 0.3 Fe2@NS was used in the oxygen-free dehydrogenation of propane to produce propylene.

[0061] The catalyst preparation method in this embodiment includes the following steps: 1) Weigh 12 g of 25% tetrapropylammonium hydroxide aqueous solution and 13 g of deionized water into a 100 mL round-bottom flask and stir evenly under 90 ℃ oil bath conditions; 2) Slowly add 15.4 g of tetraethyl orthosilicate to the above solution, and stir for 12 hours in an oil bath at 90 ℃ to obtain a clear solution; 3) Weigh 1.5 g of ammonium fluoride solid, dissolve it in 1.5 mL of deionized water, and slowly add it to the above solution. Stir evenly under 90 ℃ oil bath conditions to obtain the synthetic sol. 4) Weigh 0.642 g of ferric nitrate nonahydrate solid and 26.4 mg of chloroplatinic acid solid, and add them to the above-mentioned synthetic sol. Stir for 12 hours in an oil bath at 90 ℃ to obtain a light orange-yellow uniform sol. 5) Transfer the sol obtained in step 4) to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and hydrothermally crystallize it at 175 °C for 3 days. 6) Centrifuge the solid-liquid mixture obtained in step 5), and repeatedly wash the resulting solid with deionized water; 7) Place the solid obtained in step 6) in a forced-air drying oven at 80 ℃ and dry it at a constant temperature for 12 hours; 8) Grind the solid obtained in step 7) into powder and calcine it in a muffle furnace at 550 °C for 6 hours.

[0062] Catalyst Pt in Example 1 0.3 The characterization results of Fe2@NS are shown in Figure 1 , Figure 2 and Figure 3 . Figure 1 The XRD pattern shows that the sample has a standard molecular sieve microporous structure; Figure 2 The scanning electron microscope images show that the sample has a nanosheet morphology with a thickness of 50~100 nm and a regular structure and size. Figure 3High-resolution aberration electron microscopy and elemental analysis showed that platinum exists in the molecular sieve channels in the form of single atoms, anchored and stabilized by the framework iron. Figure 4 The carbon monoxide adsorption infrared spectroscopy showed that only CO had a linear adsorption peak, and platinum existed in the form of isolated single atoms.

[0063] catalyst Pt 0.3 The application of Fe2@NS in propane dehydrogenation reaction and the performance evaluation include the following steps: 1) Sample pretreatment and activation: The catalyst prepared above was added to the quartz reaction tube of the fixed-bed reactor and pretreated and activated at 550 °C with a 20% (v / v) hydrogen-nitrogen dilution gas. After 1 hour, the hydrogen-nitrogen dilution gas was turned off and nitrogen purging was switched to 5 minutes.

[0064] 2) Propane dehydrogenation reaction: The atmosphere was switched to propane and nitrogen dilution gas. The reaction conditions were constant temperature at 550℃, where the volume ratio of propane to nitrogen was 1:2 and the propane space velocity was 15 h⁻¹. -1 The catalytic performance of propane dehydrogenation to propylene was evaluated.

[0065] The products were separated and qualitatively and quantitatively analyzed by gas chromatography. The catalyst evaluation results are shown in Table 1.

[0066] Table 1 Pt 0.3 Single-pass conversion and selectivity of propane dehydrogenation in Fe2@NS

[0067] From Table 1 and Figure 5 As can be seen, the propane dehydrogenation catalyst of the present invention can maintain high conversion (39.7%~40.6%) and high selectivity (95.2%~98.3%) under a wide range of reaction conditions, thereby achieving 136.1 mmol C3H6·g cat -1 ·h -1 Its high propylene yield and exceptional stability, along with its extremely low deactivation rate, mean a longer service life and lower operating costs.

[0068] The catalyst Pt of this invention 0.3 Fe2@NS was applied to propane dehydrogenation reaction and its recycling performance was evaluated. The regeneration steps included: removing the spent catalyst from the reaction tube and placing it in a muffle furnace for calcination using circulating air at 550°C for 3 hours at a heating rate of 2°C per minute. The regenerated catalyst was then placed back into the quartz tube reactor for pretreatment activation and performance evaluation under the following conditions: constant temperature of 550°C, propane to nitrogen ratio of 1:1, and propane space velocity of 4 h⁻¹. -1 The catalyst evaluation results are shown in Table 2.

[0069] Table 2 Pt 0.3 Propane dehydrogenation cycle stability test of Fe2@NS

[0070] From Table 2 and Figure 6 As can be seen, the catalyst of this invention exhibits excellent regenerability and long-term stability. In continuous reactions lasting up to 150 hours and multiple cyclic regeneration tests, its catalytic activity (conversion rate ~50%) and product selectivity (>95%) both stably recovered to their initial levels. Most importantly, the regeneration process only requires calcination in circulating air, without any special atmosphere or complex steps, and is characterized by mild conditions and simple operation.

[0071] Example 2

[0072] A platinum-zinc bimetallic catalyst confined within pure silicon nanosheet molecular sieves was synthesized, using ammonium fluoride as a mineralizing agent and hydrated zinc nitrate and chloroplatinic acid as inorganic iron and platinum sources, respectively. This catalyst was named catalyst Pt. 0.1 Zn4@NS was used in the oxygen-free dehydrogenation of propane to produce propylene.

[0073] The catalyst preparation method in this embodiment includes the following steps: 1) Weigh 12 g of 25% tetrapropylammonium hydroxide aqueous solution and 13 g of deionized water into a 100 mL round-bottom flask and stir evenly under 90 ℃ oil bath conditions; 2) Slowly add 15.4 g of tetraethyl orthosilicate to the above solution, and stir evenly under oil bath conditions at 90 ℃ to obtain a clear solution; 3) Weigh 1.5 g of ammonium fluoride solid, dissolve it in 1.5 mL of deionized water, slowly add it to the above solution, and stir evenly under 90 ℃ oil bath conditions to obtain the synthetic sol; 4) Weigh 0.945 g of zinc nitrate hexahydrate solid and 9.0 mg of chloroplatinic acid solid, and add them to the above-mentioned synthetic sol. Stir for 12 hours in an oil bath at 90 °C to obtain a light yellow uniform sol. 5) Transfer the sol obtained in step 4) to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and hydrothermally crystallize it at 175 °C for 3 days. 6) Centrifuge the solid-liquid mixture obtained in step 5), and repeatedly wash the resulting solid with deionized water; 7) Place the solid obtained in step 6) in a forced-air drying oven at 80 ℃ and dry it at a constant temperature for 12 hours; 8) Grind the solid obtained in step 7) into powder and calcine it in a muffle furnace at 550 °C for 6 hours.

[0074] It will be named catalyst Pt 0.1 The application of Zn4@NS in propane dehydrogenation reaction and the performance evaluation included the following steps: 1) Sample pretreatment activation: Add 0.1 g of catalyst to the quartz reaction tube of the fixed bed reactor, and pretreat and activate the catalyst at 550 °C with a volume fraction of 20% hydrogen and nitrogen dilution gas. After 1 hour, turn off the hydrogen and nitrogen dilution gas and switch to nitrogen purging for 5 minutes.

[0075] 2) Propane dehydrogenation reaction: The atmosphere was switched to propane and nitrogen dilution gas. The reaction conditions were constant temperature at 550℃, where the volume ratio of propane to nitrogen was 1:2 and the propane space velocity was 15 h⁻¹. -1 The catalytic performance of propane dehydrogenation to propylene was evaluated.

[0076] The products were separated and qualitatively and quantitatively analyzed by gas chromatography. The catalyst evaluation results are shown in Table 3.

[0077] Table 3. Single-pass conversion and selectivity of propane dehydrogenation in Pt0.1Zn4@NS

[0078] Table 3 shows that the zeolite-zinc bimetallic catalyst confined within the molecular sieve can effectively catalyze the propane dehydrogenation reaction, exhibiting ultra-high propylene selectivity (>98%) and good propane conversion (>35%), with the highest propylene yield reaching 122.08 mmol C3H6·g. cat -1 ·h -1 .

[0079] Example 3

[0080] A platinum-manganese bimetallic catalyst confined within pure silicon nanosheet molecular sieves was synthesized using ammonium fluoride as a mineralizing agent and manganese gluconate and chloroplatinic acid as inorganic manganese and platinum sources, respectively. This catalyst was named Pt. 0.3 Mn2@NS was used in the direct dehydrogenation of propane to produce propylene.

[0081] The catalyst was prepared according to the method of Example 1, except that in step 4, 0.715 g of manganese gluconate solid was weighed instead of ferric nitrate solid. The resulting catalyst Pt 0.3 Mn2@NS was applied to the propane dehydrogenation reaction, and its performance was evaluated. The reaction conditions were a constant temperature of 550℃, a propane-to-nitrogen ratio of 1:1, and a propane space velocity of 9.6 h⁻¹. -1 The catalyst evaluation results are shown in Table 4.

[0082] Table 4 Pt 0.3 Single-pass conversion and selectivity of propane dehydrogenation in Mn2@NS

[0083] Table 4 shows that the zeolite-confined platinum-manganese bimetallic catalyst can effectively catalyze the propane reaction, exhibiting high propylene selectivity (>97%) and good propane conversion (≈35%), with a maximum propylene yield of 81.4 mmol C3H6·g. cat -1 ·h -1 .

[0084] Example 4

[0085] A platinum-indium bimetallic catalyst confined within pure silicon nanosheet molecular sieves was synthesized using ammonium fluoride as a mineralizing agent and indium hydrated and chloroplatinic acid as inorganic indium and platinum sources, respectively. This catalyst was named Pt. 0.3 In 0.6 @NS, and used it in the direct dehydrogenation of propane to produce propylene.

[0086] The catalyst was prepared according to the method of Example 1, except that in step 4, 0.134 g of indium nitrate solid was weighed instead of iron nitrate solid. The resulting catalyst Pt 0.3 In 0.6 @NS was applied to the propane dehydrogenation reaction and its performance was evaluated. The reaction conditions were a constant temperature of 550℃, a propane-to-nitrogen volume ratio of 1:1, and a propane space velocity of 9.6 h⁻¹. -1 The catalyst evaluation results are shown in Table 5.

[0087] Table 5. Single-pass conversion and selectivity of propane dehydrogenation in Pt0.3In0.6@NS

[0088] Table 5 shows that the zeolite-indium bimetallic catalyst confined within the molecular sieve can effectively catalyze the propane reaction, exhibiting high propylene selectivity (>96%) and good propane conversion (≈36%), with a maximum propylene yield of 82.5 mmol C3H6·g. cat -1 ·h -1 .

[0089] Comparative Example 1

[0090] A molecular sieve catalyst containing bimetallic platinum-iron was prepared using a ligand-protected in-situ synthesis method different from that of the present invention. Ethylenediamine was used as the metal ligand protecting agent. The procedure followed that of Example 1, except that step 3 was omitted and step 4 was replaced by: dissolving 0.642 g of ferric nitrate nonahydrate solid and 26.4 mg of chloroplatinic acid solid in a mixed solution of 1.5 mL of deionized water and 280 μL of anhydrous ethylenediamine, sonicating to obtain a pale yellow clear solution, adding this to the solution obtained in step 2, and stirring continuously for 12 hours in an oil bath at 90 ℃. The resulting catalyst was used in the direct dehydrogenation of propane to propylene, and the specific results are shown in Table 6.

[0091] Table 6. Single-pass conversion and selectivity of propane dehydrogenation in Comparative Example 1

[0092] Figure 4 The CO adsorption results showed that the PtFe bimetallic catalyst prepared by the conventional ligand protection method exhibited both linear and bridged CO adsorption peaks, confirming the heterogeneous structure of platinum species coexisting in single-atom and cluster states. This structural characteristic will have a significant negative impact on its catalytic performance. Table 6 data shows that the PtFe bimetallic pure silica molecular sieve catalyst has certain propane dehydrogenation activity, but its overall propane conversion rate is low, and its catalytic stability is poor. In a continuous 10-hour reaction test, the catalyst showed a significant activity decay trend, making it difficult to meet the requirements for long-term catalyst stability in industrial applications. This structure of coexistence of single atoms and clusters may lead to uneven distribution of active sites, poor tolerance to metal agglomeration or carbon deposition during the reaction, thereby accelerating the catalyst deactivation process.

[0093] Comparative Example 2

[0094] A bimetallic platinum-iron supported molecular sieve catalyst was prepared using a stepwise synthesis method different from that of the present invention. Specifically, an iron-confined monometallic molecular sieve catalyst (Fe2@NS) was prepared according to the method of Example 1, the difference being that no platinum source was introduced into the synthesis sol. Then, an equal mass of chloroplatinic acid was dissolved in 40 mL of deionized water to prepare a platinum impregnation solution. Fe2@NS was dispersed in the impregnation solution, and the solution was gradually evaporated to dryness in an 80 °C water bath. The resulting solid was dried and calcined to obtain the catalyst. The obtained catalyst was used in the direct dehydrogenation of propane to propylene, and the specific results are shown in Table 7.

[0095] Table 7. Single-pass conversion and selectivity of propane dehydrogenation in Comparative Example 2

[0096] Table 7 shows that although the PtFe bimetallic pure silica molecular sieve nanosheet catalyst obtained by stepwise impregnation exhibits preliminary catalytic activity in the propane dehydrogenation reaction, its overall performance is significantly limited. The propane conversion rate of this catalyst is at a low level. More notably, its reaction stability is insufficient, showing a clear trend of activity decay even in a continuous test lasting 10 hours. These performance shortcomings make it difficult to meet the requirements of long-term catalyst stability for industrial applications.

[0097] Comparative Example 3

[0098] A different impregnation method than that used in this invention was employed to prepare a supported molecular sieve catalyst containing bimetallic platinum-iron. In this method, both platinum and iron were introduced via impregnation. Equal masses of chloroplatinic acid and ferric nitrate were dissolved in 40 mL of deionized water to prepare a platinum-iron bimetallic impregnation solution. Nanosheet molecular sieves were dispersed in the impregnation solution, and the solution was gradually evaporated to dryness in an 80 °C water bath. The resulting solid was dried and calcined to obtain the catalyst. The obtained catalyst was used in the direct dehydrogenation of propane to propylene, and the specific results are shown in Table 8.

[0099] Table 8. Single-pass conversion and selectivity of propane dehydrogenation in Comparative Example 3

[0100] The results in Table 8 show that the PtFe bimetallic catalyst obtained by conventional impregnation on pure silicon molecular sieve nanosheets has significantly insufficient propane dehydrogenation activity, specifically, the propane conversion rate is less than 10%, which is difficult to meet the basic requirements for efficient catalysis.

[0101] Comparative Example 4

[0102] A supported molecular sieve catalyst containing bimetallic platinum and iron was prepared using a molecular sieve support different from that of the present invention. Specifically, a commercially pure silicon MFI molecular sieve was used as the support, and the platinum and iron bimetallic compounds were introduced by impregnation, following the method of Comparative Example 3, except that the commercially pure silicon MFI molecular sieve was dispersed in the impregnation solution. The resulting catalyst was used in the direct dehydrogenation of propane to propylene reaction, and the specific results are shown in Table 9.

[0103] Table 9. Single-pass conversion and selectivity of propane dehydrogenation in Comparative Example 4

[0104] The results in Table 9 show that the PtFe bimetallic catalysts obtained by conventional impregnation methods on commercial pure silicon molecular sieves exhibit significantly insufficient activity, making it difficult to support efficient catalytic processes and meet the basic requirements for industrial applications.

[0105] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A molecular sieve-confined metal propane dehydrogenation catalyst, characterized in that, The catalyst comprises a molecular sieve nanosheet support and a metal active component. The metal active component comprises a first metal and a second metal. The first metal exists in the molecular sieve channels in a single-atom form, and the second metal is formed around the first metal and at least partially replaces the molecular sieve framework structure. The first metal is selected from at least one of Pt, Pd, Ir, Rh and Ru, and the second metal is selected from at least one of Fe, Co, Zn, Cu, Mn, In and Ga.

2. The molecular sieve-confined metal propane dehydrogenation catalyst according to claim 1, wherein, Based on the weight of the catalyst, the content of the first metal is 0.01 wt% to 1 wt%, preferably 0.05 wt% to 0.5 wt%, more preferably 0.1 wt% to 0.4 wt%, the content of the second metal is 0.1 wt% to 20 wt%, preferably 0.2 wt% to 10 wt%, more preferably 0.3 wt% to 6 wt%, and the remainder is the support; The silicon-to-aluminum ratio of the molecular sieve nanosheet carrier is greater than or equal to 50, and it is preferably a pure silicon molecular sieve.

3. A method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization, comprising the following steps: Step 1: Mix and stir the organic structural template agent, silicon source, and water; Step 2: Mix the aqueous solution of the fluoride ion mineralizing agent with the solution obtained in Step 1, and perform the first stirring and aging to obtain the synthetic sol; Step 3: Mix the aqueous solution containing the first metal precursor and the second metal precursor with the synthetic sol, and perform a second stirring and aging process to obtain a metal-containing synthetic sol; the first metal in the first metal precursor is selected from at least one of Pt, Pd, Ir, Rh and Ru; the second metal in the second metal precursor is selected from at least one of Fe, Co, Zn, Cu, Mn, In and Ga; Step 4: Perform hydrothermal crystallization on the metal-containing synthetic sol, then perform solid-liquid separation on the mixture obtained by hydrothermal crystallization, and then dry and optionally calcine the separated solid product to obtain a molecular sieve confined metal propane dehydrogenation catalyst.

4. The method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization according to claim 3, wherein, The organic structural template agent is at least one of ethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the silicon source is at least one of silica sol, tetraethyl orthosilicate, amorphous silica, silica, and silicates; and the fluoride-containing mineralizing agent is at least one of ammonium fluoride, sodium fluoride, potassium fluoride, and calcium fluoride. The molar ratio of the organic structural template agent (in molecules) to the silicon source (in SiO2) in the synthesis mother liquor is T / SiO2 = 0.05~0.4:1, preferably T / SiO2 = 0.05~0.2:1; The molar ratio of water to the silicon source (calculated as SiO2) in the synthesis mother liquor is H2O / SiO2 = 5~100:1, preferably H2O / SiO2 = 20~50:1; The molar ratio of the ammonium fluoride (in molecules) to the silicon source (in SiO2) in the synthesis mother liquor is NH4F / SiO2 = 0.01~1:1, preferably NH4F / SiO2 = 0.05~1:1; The mixing and stirring time in step 1 is 1 to 12 hours.

5. The method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization according to claim 3, wherein, The conditions for the first stirring aging in step 2 include: a temperature of 25~100 ℃ and a time of 1~24 hours; the conditions for the second stirring aging in step 3 include: a temperature of 25~100 ℃ and a time of 1~24 hours.

6. The method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization according to claim 3, wherein, The first metal precursor is at least one of the following: inorganic acid, inorganic salt, inorganic acid salt, inorganic complex, organic acid, organic acid salt, organic complex, oxide, and hydroxide of the first metal; The second metal precursor is at least one of the inorganic acid salt, organic acid salt, oxide and hydroxide of the second metal; The inorganic acid salt is preferably a nitrate, hydrochloride, or sulfate, and the organic acid salt is preferably at least one of acetate and gluconate. Preferably, the first metal precursor is at least one selected from chloroplatinic acid, platinum nitrate, platinum chloride, dichlorotetramineplatinum, platinum acetylacetonate, chloropalladium acid, palladium nitrate, palladium acetate, tetraamminepalladium nitrate, potassium tetrachloropalladate, palladium acetylacetonate, ruthenium trichloride, ruthenium acetylacetonate, rhodium trichloride, rhodium acetylacetonate, chloroiridic acid, and potassium hexachloroiridate. Preferably, the second metal precursor is at least one of ferric nitrate, ferric sulfate, ferrous sulfate, ferrous nitrate, ferric chloride, ferrous chloride, cobalt sulfate, cobalt nitrate, cobalt chloride, zinc nitrate, zinc sulfate, zinc chloride, manganese gluconate, manganese sulfate, manganese nitrate, manganese chloride, indium nitrate, indium chloride, gallium nitrate, and gallium chloride.

7. The method for preparing a molecular sieve-confined metal propane dehydrogenation catalyst by fluorine-assisted rapid crystallization according to claim 3, wherein, In step 4, The conditions for hydrothermal crystallization include: a temperature of 90~200 ℃ and a time of 1~7 days; The drying temperature is 60~120 ℃, and the time is 6~12 hours; The roasting temperature is 500~700 ℃, the time is 2~10 hours, and the roasting atmosphere is air.

8. A molecular sieve-confined metal propane dehydrogenation catalyst prepared by the method according to any one of claims 3-7.

9. The application of the molecular sieve-confined metal propane dehydrogenation catalyst according to any one of claims 1-2 and 8 in the oxygen-free dehydrogenation of propane to propylene.

10. A method for the oxygen-free dehydrogenation of propane to propylene, characterized in that, The method is carried out in a fixed-bed reactor, wherein the catalyst bed of the fixed-bed reactor is packed with the molecular sieve-confined metal propane dehydrogenation catalyst according to any one of claims 1-2 and 8, and the method includes the following steps: Before the reaction, the catalyst is pretreated with a reducing gas or an inert gas, and then the raw material gas is introduced to carry out the propane dehydrogenation reaction. Preferably, the reducing gas is selected from at least one of diluted hydrogen and diluted carbon monoxide, and the inert gas is selected from at least one of nitrogen, argon and helium; Preferably, the pretreatment temperature is 300~600 ℃ and the time is 0.5~4 hours; Preferably, the concentration of propane in the feed gas is 10-100 wt%, more preferably 50-100 wt%. Preferably, the propane dehydrogenation reaction is carried out at a temperature of 300-650 °C, a pressure of 0-0.2 MPa, and a reaction space velocity of 1-100 h⁻¹. -1 Preferably 4~60 h -1 .

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